UPDATE 5:38 PM CST: Multiple news outlets report that the shooter was a woman in her mid-30's, and that the violence was the result of a domestic dispute. Police, however, have not officially confirmed this.

UPDATE 4:41 PM CST: At a press briefing, San Bruno Police Chief Ed Barberini said police had found a woman dead of a self-inflicted gunshot wound who they believe could be the shooter. However, he could not confirm her identity or her status as a suspect so early into the investigation. Barberini confirmed that there were at least three other casualties.

I have transcribed Chief Barberini's comments below:

At 12:46 PM this afternoon, San Bruno Police Department received numerous 9-1-1 calls regarding gun shots at the YouTube campus located on Cherry Avenue in our city. San Bruno police arrived on scene at 12:48 PM, and immediately began a search for a possible shooter or suspect.

Upon arrival, officers encountered numerous employees fleeing from the building. It was very chaotic, as you can imagine. We did encounter one victim with an apparent gunshot wound towards the front of the business as we arrived.

Several minutes later, while conducting a search of the premises, officers located a second individual with a gunshot wound that appears may have been self-inflicted. We are still working on confirming that.

Two additional victims were located several minutes later at an adjacent business. The extent of all of the injuries of our victims are unknown right now. They were all transported for emergency medical care, but they are all unknown.

We have four victims who have all been transported for gunshot related injuries, and we have one subject who's deceased inside the building with a self-inflicted wound that at this time we believe to be the shooter, but we're still following up on that.

UPDATE 4:35 PM CST: At a press conference that wrapped up just moments ago, San Francisco General Hospital Spokesman Brent Andrew confirmed that his hospital had taken in three victims - a 32-year-old woman in serious condition, a 27-year-old woman in fair condition, and a 36-year-old man in critical condition. Andrew would not comment upon the nature of their injuries, but said that a trauma surgeon would brief the press later.

UPDATE 4:07 PM CST:The Los Angeles Times reports that at least two people were transported from the YouTube HQ campus to a local hospital. We are continuing to monitor reports and will update this post as new information becomes available.

Trolls were posting photos of men and women to Twitter and claiming they depicted a suspect. So far, police have not commented on the gender or motivation of any suspect, nor have the confirmed any contact with a suspect.

Reports of an active shooter on the campus of YouTube's San Bruno, California headquarters were circulating on Twitter Tuesday afternoon, as employees described hearing gunshots and seeing colleagues being evacuated.

YouTube product manager Vadim Lavrusik tweeted that he heard shots and saw people running before he and coworkers barricaded themselves in a room.

The San Bruno Police department confirmed via Twitter than they had responded to reports of an active shooter, and were advising people to avoid the area.